Electrochemical machining (hereinbelow also referred to alternatively as simply machining) is a conventional process in which a workpiece is typically provided with a positive voltage to create an anode, and an electrode is provided with a negative voltage to create a cathode. DC voltages between about 5-25 volts and up to about 15-30,000 amps are typically used. An electrolyte is then channeled in the space or gap between the workpiece and the cathode for electrochemically machining the workpiece. Such gap must be accurately maintained to avoid damaging sparking, or arcing, which would occur with gaps which are too small or cause too little electrolyte flow during operation.
A gas turbine engine stator vane as used in compressors thereof, for example, typically include radially outer and inner shrouds formed integrally with an airfoil extending transversely therebetween. The radially inner surface of the outer shroud and the radially outer surface of the inner shroud are referred to herein as platforms which form a portion of the flowpath for confining the airflow between the shrouds and over the airfoil.
To manufacture the vane to its final dimensions, an oversized workpiece is conventionally provided and the excess material thereof is accurately removed to form the required final configurations of the airfoil and platforms. Electrochemical machining is conventionally known for simultaneously removing material from both an airfoil and one of the platforms by using a single cathode which is translated simultaneously toward both the airfoil and the platform. However, since the vane includes two platforms, it is conventionally manufactured in either two operations for machining the airfoil and one of the platforms and then the other platform, or, in one prior art apparatus, two cathodes may be used simultaneously for machining both platforms as well as the airfoil.
Since electrochemical machining utilizes the surface of the cathode to carry current between the anode and the cathode through the electrolyte, the cathode surface should be suitably configured to conform to the workpiece as close as possible to its finally required configuration and dimensions, preferably without additional manufacturing operations such as benching. Benching is a conventional operation for manual grinding or polishing of the workpiece to remove any irregularities or excess material remaining after electrochemical machining.